Hermetically sealed cell

ABSTRACT

The object of the present invention is to provide a closed battery capable of rapidly releasing the internal pressure thereof and at the same time disconnecting the current to effectively prevent a rise in temperature and explosion so that it may assure the safety and reliability of the battery, when, the internal pressure is elevated due to short circuit, overcharge, reverse charge, or the like in such a completely closed battery. 
     A closed battery of the present invention is provided with a closing member serving as a valve chip, which is composed of a metal substrate  1  in which a valve element  5  is provided and defined by a break line  3 , and a metal foil  2  adhered to the inner surface of the metal substrate  1 . When the internal pressure of the battery is elevated, the valve element  5  is raised up from the metal substrate from the bending fulcrum portion  4  so as to permit a opening valve  7  to be formed, so that the metal foil  2  is allowed to burst accurately at a prescribed pressure, especially at a low pressure, so as to discharge the internal gas of the battery. Also, with a lead wire  6  attached to the metal foil  2 , the burst can break the current so that the battery is prevented from exploding.

CROSS REFERENCE TO RELATED APPLICATION

The present application is the national stage under 35 U.S.C. 371 ofPCT/JP98/01802, filed Apr. 20, 1998.

FIELD OF THE INVENTION

The present invention relates to a closed battery capable of bursting ata prescribed pressure, especially at a low pressure, to rapidly releasethe internal pressure and at the same time to break a current, when thebattery temperature or the battery internal pressure is elevated.

RELATED ART

Recently, with increasing requirement for electronic devices that aremade into much smaller size and lighter weight with high performance,the use of non-aqueous batteries with high energy density has becomepopular. Batteries which use an alkaline metal such as lithium, sodium,or potassium as an active material for the negative electrode thereofemploy a battery container of a completely closed structure, since thealkaline metal easily acts with water.

Such a completely closed battery has the advantage of reasonablestorability, however, its high sealability sometimes causes rupture ofthe battery itself due to the abnormally elevated internal pressurethereof in a case where the battery is exposed to high temperature, orshort circuit is formed inside or outside of the battery to cause alarge flow of the current, or hydrogen gas is generated in the batterydue to water contamination penetrated in the manufacturing processthereof. In such a case, the device that accommodates such a rupturingbattery will be broken and moreover, there may be a danger of the brokendevice and battery harming the user. Accordingly, there is a need forsome pressure releasing mechanism before the internal pressure of thebattery is increased to such a high extent.

So far, several methods for releasing the internal pressure of a batteryhave been proposed and some of them have been used in practice. Forinstance, Japanese laid-open publication HEI 2-304861 discloses a safetyvalve for a battery, which comprises a valve chest provided at a part ofa container of the battery and having a valve through hole to becommunicated with the inside of the battery and an outlet to becommunicated with the outside, the valve chest comprising a valve memberat least whose surface opposed to the valve through hole is made ofrubber, and an elastic member for pushing the above mentioned rubbersurface of the valve member to the valve through hole. This safety valveholds the sealability of the battery by closing the valve through holewith the rubber-made valve member, and prevents the internal pressure ofbattery from rising in excess of a prescribed pressure by permitting thevalve through hole to be opened when the internal pressure rises to thepressure prescribed for the elastic member.

Such a conventional safety valve has been widely used in Ni—Cd typebatteries, however, it has not yet been used in the non-aqueousbatteries which employ alkaline metals as the active material for thenegative electrode, since even if the elastic member presses the valvemember to the valve through hole to thereby close the battery, it isimpossible to obtain such a high sealability as required for thenon-aqueous batteries.

One of the methods for releasing the internal pressure of a batterywhich requires high sealability is disclosed in Japanese laid-openpublication SHO 63-285859. In this method, a container of the battery isprovided with a thinned portion at a part of its wall. This thinnedportion is formed by cold rolling a sheet of the container using a pressdevice until the thickness of the rolled portion of the sheet becomeshalf of the initial thickness thereof. Thus, the battery is providedwith good sealability with regard to this thinned wall portion becauseit is only transformed from a part of the continuous wall of thecontainer.

Another pressure releasing mechanism of this type is disclosed inJapanese laid-open publication HEI-6-215760. This releasing mechanismcomprises a valve diaphragm fitted in an open end of the cylindricalcontainer of a battery having a bottom and disposed above the electrodeelement of the battery, and a lead for current cutoff disposed above thevalve diaphragm. In this structure, when the internal pressure of thebattery is elevated, the valve diaphragm is expanded to break the leadfor current cutoff to cut the current.

According to the method as disclosed in Japanese laid-open publicationSHO-63-285859, it is necessary to obtain an extremely thin wall portionof the container so that the thin portion can be ruptured at arelatively low pressure. However, when the wall portion is made toothin, there may be formed fine or minute cracks during press-forming,thus impairing the sealability of the battery container.

Further when metals are processed by cold working, their workabilitywill be inevitably harden. The hardening of the metals does not alwaystake place uniformly, and therefore, there arises a problem that theoperating pressure for such pressure releasing mechanism cannotregularly be controlled. There is also proposed a half-etching methodfor making thinner a part of the wall of a battery container, however,it is extremely difficult to control the remaining thickness of thethinned portion after etching, and also difficult to obtain a goodyield. Another problem is that the half-etched portion cannot be freefrom the formation of pinholes, and therefore, all the products need tobe inspected.

On the other hand, according to the method as disclosed in Japaneselaid-open publication HEI-6-215760, it is necessary to accuratelycontrol the depth of a cut off portion formed in the lead, which causesproblems of difficulty for cut off forming and unstable cut off of thecurrent at a prescribed pressure. Another problem is that the current isnot reliably cut off at a prescribed pressure.

SUMMARY OF THE INVENTION

With the view to solving the conventional drawbacks as mentioned above,it is the object of the present invention to provide a closed batteryincorporating a valve chip which can stably and accurately burst at aprescribed pressure, especially at a low pressure, so as to rapidlyrelease the internal pressure thereof and can be manufactured easily.

In order to solve the above-mentioned problems, the present inventionprovides a closed battery which comprises an electrode elementconsisting of a positive electrode, a negative electrode, and aseparator; an electrolyte; a battery container accommodating saidelectrode element together with said electrolyte; and a closing memberfitted in the inner periphery of an open end portion of said batterycontainer to close the open end portion of the battery container,wherein said closing member consists of a metal substrate, a valveelement which is provided in said metal substrate and defined by a breakline so as to serve as a releasing chip such that when the internalpressure of the battery is elevated, the valve element is bent from abending fulcrum so as to provide the metal substrate with an openingportion for releasing the internal pressure, and a metal foil which isadhered to the inner surface of the metal substrate.

According to the present invention, when the internal pressure of abattery is elevated due to short circuit, overcharge, reverse charge orthe like, a valve chip, consisting of a metal substrate in which a valveelement is provided for releasing the internal pressure of the batteryand a metal foil which has a uniform and accurate thickness and is laidover the metal substrate so as to close a through hole which is usuallyclosed with the valve element, operate to deform itself and push andraise the valve element up, and when the internal pressure reaches aprescribed pressure, the metal foil stably and accurately burst to cutthe electric connection and at the same time discharge the internal gaswithin the battery so that an abrupt rising of the internal temperatureor explosion of the battery can previously be prevented.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is now explained in conjunction with preferredembodiments and examples referring to the drawings.

FIG. 1 is a vertical section view showing an upper part of a completelyclosed battery of the present invention. FIG. 2 is a plane view showinga valve chip of the closed battery of the present invention. FIG. 3 is avertical section view showing the above mentioned valve chip. FIG. 4 isan explanatory view showing an operating manner of the valve chip incase of abnormality. FIG. 5 and FIG. 6 are plane views showing otherembodiments of the valve chip.

In FIG. 1, a cylindrical battery container 30 having a bottom, whichserves as a negative electrode terminal, accommodates an electrodeelement which is isolated from the outside 32 together with anelectrolyte. The electrode element 32 is composed of a coiled laminatewhich comprises a positive electrode 32 a, a separator 32 b, and anegative electrode 32 c disposed opposite to the positive electrode 32 avia the separator 32 b.

A closing cap 33, having through holes 0 and 0, which serves as arupture-preventing mechanism and at the same time as a positiveelectrode terminal is fitted by calking in the upper open end portion ofthe container 30 via an insulating gasket 34. Above the electrodeelement 32, a saucer-like inner cap 37 is disposed and a gas releasehole 35 of a large diameter is provided at the center portion of theinner cap 37.

Between the inner cap 37 and the closing cap 33, a valve chip V whichforms a closing member for enclosing the electrode element and others isprovided. A periphery 36 of the valve chip V is in contact with aperiphery 33 a of the closing cap 33. These peripheries 36 and 33 a arefixed by calking in a circumference 37 a of the inner cap 37 via aninsulating gasket 40.

A lead wire 6 is attached, by an appropriate means, to an inner surfaceof the valve chip V serving as the closing member for closing the upperopen end portion of the battery. The lead wire 6 extends to the positiveelectrode 32 a of the electrode element 32.

As shown in FIG. 2, the valve chip V is a substantially circular in aplane view, and is composed of a metal substrate 1 having a circularform and a metal foil 2 adhered to the inner surface of the metalsubstrate 1. As a material of the metal substrate 1, any one selectedfrom the group including a steel sheet, stainless steel sheet, coppersheet, and aluminum sheet may be used. As a material of the metal foil2, any one selected from the group including a steel foil, stainlesssteel foil, copper foil, aluminum foil, nickel foil, and nickel-ironalloy foil may-be used.

A substantially circular break line 3 is formed in the metal substrate 1such that the break line entirely penetrates through the metal substrate1 in its thickness direction, though the above mentioned circular linepartly leaves a non-break line portion which forms a bending fulcrumportion 4. The inner portion defined by the break line 3 is formed as avalve element 5 which is to operate as a pressure releasing chip forreleasing the internal pressure of the battery when the internalpressure is elevated. When the valve element 5 is raised up from thebending fulcrum portion 4, a valves opening portion 7 will be formed soas to release the internal pressure of the battery. (See FIG. 4.) Thelead wire 6 is attached to the metal foil 2 by brazing, for instance.

Next, an operating manner of the valve chip in case of abnormality isexplained. Once the internal pressure of the battery is elevated, thevalve element 5 is raised up, as shown in FIG. 4, from the bendingfulcrum portion 4 while breaking the metal foil 2 to thereby form thevalve opening portion 7 so that the internal pressure is releasedoutside. The gas having increased pressure passes through the valveopening portion 7 and is discharged from the through hole 0 of theclosing cap 33.

In this case, since the valve element 5 is raised up from the bendingfulcrum portion 4, the lead wire 6 is disconnected as shown in FIG. 4,or the brazed portion of the lead wire 6 to the metal foil 2 is detachedto thereby cut the electric connection.

Incidentally, the form of the valve element is not necessarily limitedto the substantially circular form as shown in FIG. 2, but the one asdenoted by 10 in FIG. 5, which is provided with an arm portion 4 a atthe bending fulcrum portion, or the one as denoted by 11 in FIG. 6,whose form is tongue-like.

According to the completely closed battery of the present invention,when the internal pressure of the battery is elevated due to someabnormality such assort circuit, overcharge, or reverse charge, themetal foil 2 bursts at a prescribed pressure stably and accurately,especially at a low pressure, to push up the circular valve element 5from the bending fulcrum portion 4 formed on the flexible metalsubstrate, wherein the circular valve element 5 is provided in theflexible metal substrate 1 and defined by the break line 3 penetratingthrough the entire thickness of the metal substrate 1. As a result, thelead wire 6 is cut off to thereby disconnect the electric connection. Asillustrated in FIG. 4 for explaining the operating manner of the valvechip in the cross section view, when the valve chip operates, it permitsthe valve opening portion 7 to be formed to thereby release the internalgas of the battery. Thus, the battery can previously be prevented fromthe abrupt rising of the internal temperature or an explosion thereof.

The operating pressure for the valve chip can be controlled within astable pressure range by selecting the material composition of the valvechip and adjusting the length of the bending fulcrum portion 4 becausemetal foil 1 can be manufactured with the highest accuracy of itsthickness in micron order.

As mentioned above, according to the present invention, when theinternal pressure of a battery is elevated due to short circuit,overcharge, reverse charge, or the like, and, it reaches a prescribedpressure, the valve chip can operate to permit the metal foil to burststably and accurately even at a low pressure so as to release theinternal gas of the battery. Thus, the battery can previously beprevented from the abrupt rising of the temperature or explosionthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section view showing an upper part of thecompletely closed battery according to the present invention.

FIG. 2 is a plane view showing the valve chip according to the presentinvention.

FIG. 3 is a vertical section view showing the valve chip according tothe present invention.

FIG. 4 is an explanatory view showing the operating manner of the valvechip in case of abnormality.

FIG. 5 is a plane view showing another embodiment of the valve chipaccording to the present invention.

FIG. 6 is a plane view showing still another embodiment of the valvechip according to the present invention.

EXPLANATION OF REFERENCE CHARACTERS

1: flexible metal substrate

2: metal foil

3: break line

4: bending fulcrum portion

5: circular valve element

6: lead wire

7: valve opening portion

What is claimed is:
 1. A closed battery system comprising: an electrodeelement consisting of a positive electrode, a negative electrode, and aseparator; an electrolyte; a battery container accommodating saidelectrode element together with said electrolyte; and a closing memberfitted in the inner periphery of an open end portion of said batterycontainer to close the open end portion of the battery container;wherein said closing member consists of a metal substrate, a valveelement which has a substantially circular form and is provided in saidmetal substrate and defined by a break line so as to serve as areleasing chip such that when the internal pressure of the battery iselevated, the valve element is bent from a bending fulcrum provided withan arm portion so as to provide the metal substrate with an openingportion for releasing the internal pressure, and a metal foil which isadhered to the inner surface of said metal substrate.